肝素通过抑制一氧化氮合酶和转化生长因子-β/Smad信号转导途径减轻脂多糖致大鼠急性肺损伤

Heparin attenuates lipopolysaccharide-induced acute lung injury by inhibiting nitric oxide synthase and transforming growth factor-β/Smad signaling pathway

目的：探讨肝素对脂多糖（LPS）致急性肺损伤（ALI）的保护作用及可能机制。方法32只SD大鼠按随机数字表法分为对照组、肝素对照组、模型组和肝素治疗组，每组8只。采用气管内滴入LPS 1 mg/kg的方法制备大鼠ALI模型，对照组和肝素对照组滴入等量生理盐水；肝素对照组和肝素治疗组于制模后每小时静脉注射肝素50 U/kg。24 h后各组大鼠进行肺泡灌洗，采用酶联免疫吸附试验（ELISA）检测支气管肺泡灌洗液（BALF）中炎症介质表达；取肺组织，测定肺湿/干质量（W/D）比值，光镜下观察肺组织病理改变，并检测其丙二醛（MDA）、一氧化氮（NO）和髓过氧化物酶（MPO）水平；反转录-聚合酶链反应（RT-PCR）检测肺组织诱导型一氧化氮合酶（iNOS）mRNA表达；蛋白质免疫印迹试验（Western Blot）检测肺组织iNOS、转化生长因子-β1（TGF-β1）和磷酸化Smad表达；免疫组化法检测肺组织iNOS表达。结果光镜下观察对照组和肝素对照组肺组织结构完整、肺泡腔清晰；模型组肺泡壁增厚，有明显的炎性细胞浸润、肺泡出血和结构破坏；肝素治疗组病理改变较模型组明显减轻。与对照组和肝素对照组比较，模型组肺W/D比值，肺组织MDA、NO、MPO，BALF中肿瘤坏死因子-α（TNF-α）和白细胞介素-6（IL-6）水平均明显升高。与模型组比较，肝素治疗组肺W/D比值，肺组织MDA、NO、MPO，BALF中TNF-α和IL-6水平均明显降低〔W/D比值：7.54±0.17比10.69±0.15，MDA（mmol/mg）：2.01±0.30比2.51±0.25，NO（μmol/L）：3.07±0.21比3.89±0.14，MPO （U/g）：1.94±0.09比2.74±0.20，TNF-α（μg/L）：201.80±0.27比297.53±0.34，IL-6（μg/L）：38.41±0.25比46.31±0.31，均P＜0.05〕。RT-PCR结果显示，肝素治疗组iNOS mRNA表达明显低于模型组（2-ΔΔCt：3.04±0.18比4.37±0.15，P＜0.05）。Western Blot检测结果显示，与对照组比较，模型组肺组织iNOS、TGF-β1蛋白表达及Smad2、Smad3磷酸化水平明显增加；而肝素治疗组蛋白表达较模型组明显受到抑制。免疫组化结果显示，肝素治疗组肺泡上皮细胞和微血管内皮细胞iNOS阳性细胞表达较模型组明显减少。结论肝素能通过抑制一氧化氮合酶的表达和TGF-β/Smad信号转导途径来发挥对LPS致大鼠ALI的保护作用。

Objective To investigate whether heparin has a beneficial effect on lipopolysaccharide（LPS）-induced acute lung injury（ALI）in rats,and to explore the possible underlying mechanisms. Methods Thirty-two adult Sprague-Dawley（SD）rats were randomly assigned into the control,heparin control,model,and heparin treatment groups,with 8 in each group. ALI rat model was reproduced by intratracheal instillation of LPS at a dose of 1 mg/kg. The rats in the control and heparin control groups received an equal volume of normal saline at the same times. The rats in the heparin control and heparin treatment groups were intravenously received 50 U/kg heparin every 1 hour after the induction of ALI. Animals were sacrificed 24 hours after LPS challenge. Bronchoalveolar lavage fluid（BALF） and lung tissue samples were collected. Histopathological evaluation,lung wet/dry（W/D）ratio,malondialdehyde （MDA）,nitric oxide（NO）and myeloperoxidase（MPO）were analyzed. Enzyme-linked immunosorbent assay（ELISA） was used to measure the concentration of inflammatory factor in BALF. Expression of inducible nitric oxide synthase （iNOS）mRNA in the lung of rats was measured by reverse transcription-polymerase chain reaction（RT-PCR）. Western Blot was used to determine the expression of transforming growth factor-β1（TGF-β1）and phosphorylation of Smad in the lung tissues. The expression of iNOS in lung was determined by immunohistochemistry. Results In the control and heparin control groups,lung tissue showed a normal structure and clear pulmonary alveoli under a light microscope. In the model group,ALI characters such as extensive thickening of the alveolar wall,significant infiltration of inflammatory cells,demolished structure of pulmonary alveoli,and hemorrhage were found. In the heparin treatment group,heparin treatment markedly alleviated LPS-induced these pathological changes in lung. Compared with control and heparin control groups,lung W/D ratio,lung MDA,NO and MPO levels,and tumor necrosis factor-α（TNF-α） and interleukin-6（IL-6）in BALF in the model group were increased significantly. Compared with the model group, lung W/D ratio,lung MDA,NO and MPO levels,and TNF-αand IL-6 in BALF in the heparin treatment group were significantly decreased〔W/D ratio：7.54±0.17 vs. 10.69±0.15,MDA（mmol/mg）：2.01±0.30 vs. 2.51±0.25,NO （μmol/L）：3.07±0.21 vs. 3.89±0.14,MPO（U/g）：1.94±0.09 vs. 2.74±0.20,TNF-α（μg/L）：201.80±0.27 vs. 297.53±0.34,IL-6（μg/L）：38.41±0.25 vs. 46.31±0.31,all P〈0.05〕. RT-PCR showed that the expression of iNOS mRNA in the heparin treatment group was significantly lower than that in the model group（2-ΔΔCt：3.04±0.18 vs. 4.37±0.15,P〈0.05）. Western Blot showed that compared with control group,the protein expressions of iNOS and TGF-β1,and phosphorylation of Smad2 and Smad3 were significantly increased,and the heparin could inhibit the protein expressions compared with model group. Immunohistochemistry showed that positive expressions of iNOS in alveolar epithelial cell and capillary endothelial cell in the heparin treatment group were significantly lower than those in the model group. Conclusion Heparin significantly ameliorated the lung injury induced by LPS in rats via the inhibition of nitric oxide synthase expression and the TGF-β/Smad pathway.